Increased environmental concerns have created a demand for new and better methods for treating a great variety of waste streams. Of particular concern are waste streams which contain constituents known to damage human health or ecosystems, such as hazardous metals, radioactive materials, hazardous organic compounds, and combinations of the like. If ingested, even low levels of many of these materials have been shown to have adverse and tragic effects on both human health, as well as the health of plants and animals in exposed ecosystems. Unfortunately, these hazardous materials are present in a great variety of industrial and consumer products, or as a by-product incident to the manufacture of industrial and consumer products or other industrial processes. Also, often times many of these hazardous substances will exist in a mixture with other, more benign waste, necessitating either costly separation of the wastes, or introducing complications for treatment of the aggregate through means such as incineration.
In many cases these hazardous substances are, or through decomposition or treatment means such as incineration may become, highly soluble in ground water or directly released into the air, greatly increasing the likelihood of their eventual introduction into, and migration within, the environment. Many of these hazardous compounds will remain in the environment in a hazardous condition indefinitely. Others will actually accumulate and concentrate through ecological mechanisms, increasing their potency. Thus, preventing the introduction of a great variety of hazardous materials and mixtures into the environment presents a great challenge for the human race, as a failure to find safe and effective waste treatment and disposal methods promises to have far reaching and disastrous consequences.
One particular strategy for safe and effective treatment and storage of such hazardous materials is "vitrification." Materials are vitrified when they are combined with glass forming materials and heated to high temperatures. In this manner, many of the hazardous constituents, such as hazardous organic compounds, are destroyed by the high temperatures, and may actually be recovered as clean burning fuels and converted into energy. In addition to the recovery of these clean burning fuels, when properly constructed, vitrification processes may be designed to reduce total gas emissions to a fraction of the levels associated with incineration, greatly simplifying gas cleanup and energy recovery. Other hazardous constituents, which are able to withstand the high temperatures without becoming volatilized, may be made to form into a molten state which then cools to form a stable glass. By carefully controlling the vitrification process, the resulting vitrified glass may be made to demonstrate great stability against chemical and environmental attack, with a high resistance to leaching of the hazardous components bound up within the glass. Hazardous constituents not converted to energy by the vitrification process are thus bound within the resulting glass, preventing the release of both into the environment or groundwater where they may be ingested by humans and wildlife. Thus, a great advantage of vitrification as a waste treatment option is vitrification's ability to treat a great variety of waste streams, including hazardous waste streams, simultaneously and satisfactorily.
Several techniques for vitrifying materials have arisen as the advantages of vitrification have become apparent and problems related to each particular approach have been addressed. The use of high temperatures and the formation of glass in the development of vitrification technologies has insured that practitioners have borrowed methods and techniques from both the metallurgical and steel making fields as well as the glass making field. In particular, the use of a variety of different heating methods and sources, as well as the use and development of refractory materials, have been critical aspects of the success of many of these vitrification processes. Common to many of these arts is a need for drain systems to remove molten materials from refractory lined heating vessels. Due to the high temperatures associated with the material, the drain through which the molten material flows in any high temperature process is subject to high levels of corrosive and mechanical wear. The chemical properties of the molten materials passing through the drain may also be particularly corrosive, exacerbating the problem.
As vitrification technologies for the treatment of waste have progressed, one interesting development has been the ability to separate and recover valuable metals contained within the various waste streams. When waste containing certain valuable metals is vitrified under the correct conditions, the metals, or a portion thereof, can be made to be insoluble in the vitreous glass which forms. In this manner, the metals will separate from the vitreous glass, and the two will form separate layers within the vitrification chamber. Just as oil will float on water, the molten vitreous glass may separate above the molten metals contained within vitrification chamber. Not surprisingly, separating the molten glass layer from the molten metal layer can present quite a challenge. Draining the materials away from each other requires separate drains for the two layers; one placed in the bottom of the heating vessel and one placed in the side wall of the heating vessel. It is also necessary that the drains be controlled, that is, the flow of the molten materials must be stopped and started, yet the drains must also be to operate in the extremely hostile environment. Prior art drain systems have also suffered from clogging. For example, in many systems it is desirable to limit the flow of the molten material at some predetermined maximum level. This may be accomplished by limiting the circumference of the aperture in the drain tube. Problems arise when chunks of waste materials which have not been completely rendered into a molten state clog these drain tubes. These and other requirements have created a need for better drains to handle the flow of molten materials generated in high temperature applications such as vitrification waste treatment schemes.